Wireless charging uses an electromagnetic field to transfer energy from a charging device (such as a charging station) to an inductively coupled electronic device (such as a wearable device, smart phone, or the like). Typically, an inductive coil within the charging device (a “transmitter”) generates a time-varying electromagnetic field from, for example, an alternating current (AC) flowing through the coil. This field generates a corresponding time-varying current within a second inductive coil in the electronic device (a “receiver”) by way of electromagnetic induction, and the electronic device can use this generated current to charge its battery. The transmitter and receiver inductive coils in proximity to each other effectively form an electrical transformer. Generally, the inductive coils must be in close proximity for power to be transferred. As the distance between the coils increases, power transfer becomes less efficient.
The proximity requirement can be especially problematic for electronic devices and their charging stations having three-dimensional (e.g., curved) charging surfaces. Inductive charging coils generally have a planar geometry. Thus, when a conventional coil is disposed along a non-planar charging surface of an electronic device or charging station, portions of the coil may be positioned some distance from the surface. This increases the distance between portions of the transmitter and receiver coils, thereby reducing wireless charging efficiency.
In one existing solution, wound coils have been designed where a wire is physically wound about an object having the desired three-dimensional geometry. Such processes, however, are time consuming and are associated with low precision of coil geometry and wire spacing, thereby resulting in undesirable losses in charging efficiency.